Inhibition of IGF-1R: A therapeutic strategy to inhibit colon cancer stem-like cells PD/PI: Patel, Bhaumik B. PROJECT DESCRIPTION Abstract: Despite recent advances in therapeutics, colorectal cancer remains the third deadliest cancer in the USA. This is mainly attributable to survival of a small population of cancer cells called stem cells (CSCs), which display dysregulated self-renewal, aberrant differentiation at the cellular level, and resistance to most cancer chemotherapies preventing complete cure of cancer. Others and we have shown that inhibition of IGF-1R- AKT-mTOR (InAT) axis is a promising approach to target this resistant population within the tumors. However, this promise has not lived up to the high expectations. We have uncovered a novel, critical and clinically relevant mechanism of IGF-1R inhibition's effect on CSCs that involves downregulation of mevalonate- isoprenoid biosynthesis (MIB) pathway, a precursor pathway of steroid synthesis, at levels distal to that targeted by statins, th widely used anti-cholesterol drugs. Inhibition of MIB pathway results in depletion of several bioactive terpenes that are involved in critical biological processes such as protein prenylation and N- Glycosylation, which in turn regulates -catenin signaling, a critical pathway governing colonic CSCs growth. We hypothesize that that a combination strategy employing simultaneous inhibition of InAT axis and MIB pathway, with FDA-approved agents or those that are in advanced clinical development, will results in synergistic downregulation of MIB pathway, -catenin signaling, and CSCs growth. This hypothesis will be tested in three specific aims. In vitro and in vivo models of CSCs as well as utilizing primary human colon cancer samples, we will establish significance of InAT axis and MIB pathway upregulation on CSCs growth (Aim 1). Subsequently, we will determine optimal therapeutic combination(s) of select agents from targeting InAT axis combined with those that suppress MIB pathway by employing sequential strategy of in vitro screening of the proposed drug combination in 10 selected colon cancer cell lines, with diverse genetic changes representing sporadic CRC, to identify highly synergistic combinations that will be advanced in animal models of CSCs growth (Aim 2). Moreover, we will examine detailed molecular mechanisms of inhibition of InAT axis (alone or in combination with a MIB pathway inhibitor, also 'optimum anti-CSCs combination(s)') on MIB pathway downregulation as well as CSCs growth by employing advanced biophysical and biochemical studies to a) determine levels of mevalonate pathway metabolites, b) determine the role of InAT-SREBP axis in regulating gene specific transcription of MIB pathway enzymes, and c) examining the role of downstream terpene molecules (which regulate prenylation and N-glycosylation) in regulating -catenin/TCF-4 signaling (Aim 3). The results from the proposed experiments would greatly expand our understanding of mechanisms of colon CSCs growth and identify 'optimum anti-CSCs combination(s)' therapy that will be immediately testable in the clinical trial(s), and will have paradigm-shifting implications in the treatment of colorectal cancr. 1